WASHINGTON — Satellite imagery indicates North Korea has been testing rocket engines, a sign it continues to develop its long-range ballistic missiles, a U.S. academic institute said Monday.

The analysis provided to The Associated Press is based on satellite images taken as recently as late September of the Sohae site on the secretive country’s northwest coast. In April, the North launched a rocket from there in a failed attempt to propel a satellite into space in defiance of a U.N. ban.

The analysis on the website of the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies, which is called “38 North,” said it remains unclear whether the North is preparing another rocket launch but predicted it may embark on new rocket and nuclear tests in the first half of 2013.

The analysis underscores the challenges posed by the North’s weapons programs to the United States and its allies as President Barack Obama heads into his second term. Washington’s most recent attempt to negotiate a freeze in the North’s nuclear program and a test moratorium in exchange for food aid collapsed with the April launch that the U.S. regarded as a cover for testing ballistic missile technology.

In 2009, North Korea tested a long-range missile and its second nuclear weapon within months of Obama taking office, and the 38 North analysis says North Korea may conduct new tests in the aftermath of presidential elections recently completed in U.S. and due in December in South Korea. That could be viewed as a tactic to exert more pressure on the close allies as the North seeks recognition as a nuclear power.

Last month, Defense Secretary Leon Panetta said North Korea continues to prepare for such tests, and the North, angered by Washington’s recent agreement to let Seoul possess missiles capable of hitting all of its territory, has recently claimed that the U.S. mainland is within range of its missiles.

More in News

The CIA has concluded in a secret assessment that Russia intervened in the 2016 election to help Donald Trump win the presidency, rather than just to undermine confidence in the U.S. electoral system, according to officials briefed on the matter.

A costly and burdensome permitting process pushes people into underground spaces, where the desire for inclusion sometimes outweighs safety concerns, say musicians and venue operators involved in the East Bay’s DIY music scene.

Thirty-six people — musicians, artists, students, lovers and friends — lost their lives on Dec. 2, 2016, in the fire that consumed the Oakland warehouse known as the “Ghost Ship.” Here are their stories.